Need Help on modding units

Hi Guys,

I have played MTW2 (excellent game). I want to add a unit to Portugal (Longbowmen) to make their playing style complete. I have read through all of the threads and guides and have run the unpacker, recovered it from Vista and have edited the export_descr files for both units and buildings to include Portugal as a faction that gains access to Longbowmen.

Now to the problem - and I am sorry as this has probably been answered many times before and is probably quite boring, but I need some assistance.

I modified the 2 files listed above and then saved them, but left the files where they originally were in the SEGA/MTW2/data folder - is this right? (I appreciate I have changed the original rather than creating a new folder).

The game is still not allowing me to build Longbowmen in Portugese castles. The system is not registering these changes.

I have tried adding the command:
[io]
file_first = true

to the beggining of the medievel2.preferences.cfg file but it still does now work (also tried adding to the end just in case)

Any suggestions? Am I missing something?

Any help would be greatly appreciated as this is becoming an irritation and I am turning to drink!

Many thanks in advance for any help provided.